Combustion products detector assembly and method of operation

ABSTRACT

An air inlet assembly for directing air into an ion chamber of a combustion products detector of the ionization chamber type comprises a shallow flat bottomed cup opening toward an open ion chamber and acts as a closure for completing the chamber; the cup has in its side wall radial slots for directing air flowing in from any side toward the center axis of the cup, a hole in the cup bottom at the central axis utilizes the velocity effect of the air crossing the inside of the cup to draw air in transversely and direct air into the ion chamber. A conducting screen on the cup adjacent the slots restricts somewhat the air flow somewhat and acts as an ion collector. The ion chamber is a right circular cylinder and has a conducting plate on its bottom wall and a radioactive alpha emitter source at the center of the plate; an electric potential is applied to produce a field extending between the plate and the screen and distributed over the chamber cross section.

United States Patent [1 1 Lehsten 1 Sept. 2, 1975 COMBUSTION PRODUCTSDETECTOR ASSEMBLY AND METHOD OF OPERATION George S. Lehsten, Englewood,Colo.

[73] Assignee: Fire Alert Company, Wheat Ridge Colo.

221 Filed: Apr. 20, 1973 211 App]. No.: 352,975

[75] Inventor:

lrinmry limminer-James W. Lawrence Aszsixlunr I;'.\'aminerDavis L.Willis Attorney, Agent, or Firm-Wm. Griffith Edwards [57] ABSTRACT Anair inlet assembly for directing air into an ion chamber of a combustionproducts detector of the ionization chamber type comprises a shallowflat bottomed cup Opening toward an open ion chamber and acts as aclosure for completing the chamber; the cup has in its side wall radialslots for directing air flowing in from any side toward the center axisof the cup, 21 hole in the cup bottom at the central axis utilizes thevelocity effect of the air crossing the inside of the cup to draw air intransversely and direct air into the ion chamber. A conducting screen onthe cup adjacent the slots restricts somewhat the air flow somewhat andacts as an ion collector. The ion chamber is a right circular cylinderand has a conducting plate on its bottom wall and a radioactive alphaemitter source at the center of the plate; an electric potential isapplied to produce a field extending between the plate and the screenand distributed over the chamber cross section.

13 Claims, 4 Drawing Figures OOOOOOOOOOOOOOOOUO COMBUSTION PRODUCTSDETECTOR ASSEMBLY AND METHOD OF OPERATION This invention relates to thedetection of products of combustion in the atmosphere and particularlyto an improved method and apparatus for effectively sampling the air ina room or other enclosure.

Many smoke or combustion product detectors have been provided heretoforewhich employ ionization chambers through or over which the ambient airis circulated for sampling and operation of an indicating device oralarm upon the occurrence of a predetermined concentration of combustionproduct in the air. These devices have proved useful for manyapplications, however, it has proved difficult to obtain uniform andreliable operation in other installations of the detectors. It isdesirable to provide greater reliability and accuracy in the operationof combustion product detectors and accordingly it is an object of thepresent invention to provide a combustion product detector including animproved arrangement for effecting reliable sampling of the ambient airthrough a wide range of air flow directions and rates of movement.

It is another object of this invention to provide an improved combustionproduct detector of the type employing an ion chamber for sensing thepresence of combustion product in the ambient air.

It is another object of this invention to provide an improved air inletassembly for combustion product detectors of the ionization chambertype.

It is a further object of this invention to provide an improvedionization chamber arrangement for combustion product detectors.

Briefly, in carrying out the objects of this invention in one embodimentthereof, an ionization chamber assembly is provided which comprises aright circular cylindrical chamber formed of insulating rigid syntheticplastic and an air intake assembly arranged to admit air and direct itradially toward the central axis of the chamber. Air is further causedto flow axially of the chamber and direct a portion of the air towardthe cylindrical chamber which contains a radioactive element foremitting alpha particles for ionization of air. A metal screen in theintake assembly restricts the maximum rate of flow of air into thechamber and also acts as the ion collecting plate of the device. Thedimensions of the ion chamber are proportioned to optimize thesensitivity of the detector.

The features of novelty which characterize this invention are pointedout with particularity in the claims annexed to and forming a part ofthis specification. The invention itself, however, both as to itsorganization and its method of operation, together with further objectsand advantages thereof, will best be understood by reference to thefollowing description taken in connection with the accompanying drawingsin which:

FIG. 1 is a somewhat diagrammatic elevation view partially broken awayofa device embodying the invention;

FIG. 2 is a side elevation view of the ionization chamber assembly ofthe device;

FIG. 3 is a sectional view of the device as shown in I FIG. 2; and

FIG. 4 is a top plan view of the device partially broken away.

Referring now to the drawings, the combustion products detector shown inFIG. I has been illustrated in its position for ceiling mounting. Thedetector is of the ionization chamber type and includes a referencechamber 10 and a sampling chamber 11 mounted on a printed circuit board12 which is supported within a housing l3 on suitable studs or spacersM. An intake air assembly 15 embodying the present invention is mountedon the housing 13 in axial alignment with the sampling chamber 11 andwith the sampling chamber forms the ionization chamber for detectingchanges in the density of combustion products in the ambient air.

The reference chamber 10 is closed by a metal cap or corner plate 16which'acts as the ion collector during operation of the device. Thechambers 10 and 11 are provided with buttons or discs containingradioactive material which provide the sources of alpha particles forionization of air or other gas within the chambers. The radioactivediscs are mounted on conducting posts which extend outside the chamberwalls and are indicated at 17 and 18 for the chambers 10 and 11,respectively; the disc for the chamber 11 is indicated at 18a in FIG. 3.Flat circular conducting plates are provided in the chambers in faceengagement with the bottom walls thereof and concentric with thecylindrical chambers, the plate for the chamber 11 being indicated at18b in FIG. 3. These plates cover substantially the entire bottom wallsand are in conducting relationship with the respective discs of theplates. An electric potential is applied across the chambers, theconnections for applying these potentials being made to the post 17 andthe cover plate 16 for the chamber 10 and the post 18 and the conductingscreen 20 for the chamber 11. The electrical field produced by thepotential difference between the screen 20 and the source is distributedover the cross sections of the chambers by the conducting plate 18b ofthe chamber 11 and the corresponding plate (not shown) in the chamber10. The electric circuitry for applying the potentials to the chambers10 and 11 and for detecting changes in the density of combustionproducts in the chamber in the ambient air are not essential to anunderstanding of the present invention and the circuit details havetherefore not been illustrated in the drawing.

The combustion product detector illustrated in FIG. 1 senses changes inthe combustion product density in the ambient air which reaches theinterior of the chamber through the air inlet assembly 15. The ambientair is normally in circulation due to convection currents or to airmoving devices in the area in which the detector is located. The airinlet assembly 15 is arranged to assure admission of ambient air to thesampling chamber regardless of the direction in which the air is moving.The details of construction of the air admitting assembly are shown inFIGS. 2, 3 and 4. The chamber 11 includes a block or body 21 of rigidsynthetic plastic material such as clear tempered styrene. The block isprovided with concentric annular rings or shoulders 22 and 23 whichafford mounting of the cylinder on printed circuit boards or the like inany one of three different positions on either side of the board, thetwo end p0rtions being of the same diameter are fitted in holes of thatdiameter in the printed board; the midportion determined by the diameterof the ring 22 requires a larger opening. The single cylinder 11 maythus be mounted in a relatively wide range of positions and its use in.connection with printed circuit boards is thus flexible. Chamber 11 asillustrated in FIGS. 2 and 3 is enlarged by a relatively shallow rightcircular cupped recess 24 formed in the closure 15 and which is alignedwith the axis of the chamber 11 and forms a part of the chamber. Acupped metal screen is mounted adjacent the inner walls of the recess.Ambient air as it moves over the closure plate 15 enters the innercupped recess through radial slots formed in the edge wall of theclosure 15 and communicating with the interior thereof. It will thus beseen that air flowing directly across the closure 15 from one side tothe other will enter slots on the one side, be directed generally towardthe center of the cup and then leave through slots on the other side.Air moving directly toward the closure 15 axially thereof will enterthrough the slots 25 and also will enter through a central passage 26 ofrelatively small diameter. The rate at which air may enter through theslots 25 and the passage 26 is restricted by the screen 24 which limitsthe rate of flow of air into the ionization chamber. The screen extendsbeyond the opening of the cup a distance equal to the raised portionsindicated at 27 and 28 to which the screen is secured on a collar 30which has been illustrated as having a flange 31 to which the screen iswelded, soldered or otherwise suitable secured. The flange 31 isprovided with openings to afford passage of air therethrough, and theseopenings and the screen limit the rate of air flowing through the spacebetween the housing 13 and the closure 15 provided by the raisedportions 27 and 28. A flow of air through this space may for example beproduced when air is moving directly against the plate 15 and theopenings thus provide a relief of pressure within the chamber andprevent the building up of pressure. The passage 26 centrally of theclosure plate 15 admits air to the interior of the ionization chamberwhen air is flowing across the plate 15 from one side to the otherthereof. This admission of air through the passage 26 is effected by thevelocity of the air passing the interior end of the passage 26 whichproduces a reduced pressure whereupon the air flows through the passagetransversely of the flat bottomed wall of the cup and directs some airinto the ionization chamber for circulation therein and thus assures areliable sampling of the ambient air. It will be apparent that,regardless of the direction and movement of air over the closure plate15, a portion of the air will be admitted to the interior of theionization chamber where it is to be sampled. Movement of the air in theroom thus will assure accurate sampling by providing a fresh supply ofair as long as such movement continues. It will readily be apparent thatthe detector may be placed in any desired position on the sidewall,ceiling or other surface within an enclosure such as a room and willsample the condition of the air at such location, regardless of thedirection of movement of the air within the room and also over a widerange of velocities of such movement, the screen restricting the rate offlow into the ionization chamber at the higher velocities.

For purposes of mounting the collector plate assembly or closure 15 in aunit such as illustrated in FIG. 1 holes 32 and 33 are provided whichextend through the flange of the closure plate and lie within the edgesof raised portions 27 and 28. Thus the studs 14 on which the assembly 15is mounted provide an attaching arrangement which also secures thescreen in place on the assembly. The screen 20 serves two functions,first as the ion collector plate of the ionization chamber and second.as an air flow restrictor.

The plastic bodies for the ionization chambers as in dicated at 10 andll are identical in size although the actual chambers are somewhatlarger, the chamber 10 being enlarged by the spacing of the conductingcorner plate 16 which extends beyond the edge of the plastic body, andthe chamber 11 being extended by the closure plate assembly 15 asdescribed above. By way of example, but not by way of limitation, it hasbeen found that by constructing the chamber blocks 10 and 11 so thatthey have an interior right cylindrical chamber one inch in diameter,seven-eighths inch long and extending the chamber 10 about one-eighthinch to provide an enclosed chamber of 1 inch by 1 inch and the chamberII by about three-eighth inch highly satisfactory proportions of theionization chambers are provided. The chamber 11 cooperates effectivelywith the inlet closure assembly 15 to assure accurate operation of thedetector over a wide range of different ambient air conditions in theroom or other closure in which the unit is installed.

While the invention has been disclosed in connection with a specificapplication thereof, various other modifications will occur to thoseskilled in the art. Therefore it is not desired that the invention belimited to the details illustrated and described and it is intended, bythe appended claims, to cover all modifications which fall within thetrue spirit and scope of the invention.

I claim:

1. An ambient air admitting closure member for the ionization chamber ofa combustion product detector comprising:

a rigid body having a flat portion and a'rim therearound forming acupped recess therein for providing one end portion of an ionizationchamber,

said body having a passage extending through said flat portion centrallythereof and providing communication between said recess and the ambientair and a plurality of slots spaced around said rim and entering theside of said recess, each of said slots being of a configuration forcausing ambient air moving toward one side of said body in a path normalto the central axis of said chamber and entering said slots to flow overthe surface of said flat portion and radially inward toward said centralpassage whereby the ambient air from the outside of said body will flowpast the inner end of said passage and produce a flow of air throughsaid passage into said recess transversely of the radial flow of airthrough said slots and whereby when ambient air flows axially againstsaid chamber it will be admitted through said passage and flow from saidcup recess toward said other end of the ionization chamher.

2. The invention as set forth in claim 1 wherein said flat and rimportions are circular and said slots extend radially into said recess.

3. The invention as set forth in claim 1 wherein said slots extendthrough the outer periphery of said flat portion and afford passage ofair directly therethrough when flowing along paths normal to said flatportion.

4. The invention set forth in claim 2 wherein said slots are equallyspaced about said rim and tend to direct air across said passageregardless of the direction of flow of the ambient air.

5. The invention as set forth in claim 1 including means providingadditional peripheral openings into the chamber adjacent said slots andshielded externally therefrom for affording a release of air from thechamber.

6. The invention as set forth in claim 1 including conducting meansabout said recess for providing an ion collector plate for the detector.

7. The invention as set forth in claim 1 having a cup shaped foraminousmember within said cup adjacent the walls thereof for limiting the rateof passage of air through said slots.

8. The invention as set forth in claim 7 wherein said foraminous memberis a metal screen.

9. The invention as set forth in claim 8 including means providing aninsulated wall chamber opening toward said cup and having a radiationsource therein, and means for producing an electric potential differencebetween said screen and said source for directing ions toward saidscreen whereby said screen constitutes an ion collector plate.

10. The invention as set forth in claim 9 wherein said chamber iscylindrical, and including a circular conducting plate covering a majorportion of the bottom wall of said chamber and in conductingrelationship with said source whereby the electrical field produced bysaid potential difference is distributed over the cross section of saidchamber.

11. An ion chamber for combustion product detectors and the likecomprising:

a body of electric insulating material having a right circularcylindrical chamber therein open at one end and having a flat bottomwall closing its other end, and

a flat circular plate in face engagement with said other end concentricwith said cylinder, and means providing a source of alpha particles atthe center of said circular plate.

wherein said circular plate covers the entire area ofi said bottom wall,12. An ion chamber for combustion product detectors and the likecomprising:

a body of electric insulating material having a right circularcylindrical chamber therein open at one end and having a flat bottomwall closing its other end, and

Ya flat circular plate in face engagement with said other end concentricwith said cylinder, and means providing a source of alpha particles atthe center of said circular plate,

wherein the length of said cylindrical chamber is approximately the sameas the diameter thereof and the length of the ion chamber isapproximately 1 A times the diameter of said cylindrical chamber.

13. An ion chamber assembly for apparatus utilizing a radioactivesubstance for detecting the presence of combustion products intheambient air comprising:

a. a body of insulating material having a chamber therein open at oneend,

b. a closure member for said open end, said member having a shallowright cylindrical recess providing a flat end wall,

c. means for holding said body and said member in assembled relationshipwith said chamber and said recess in open communication and forming asubstantially closed ion chamber,

d. a radioactive source in said first mentioned chamber,

e. the side wall of said closure member having a plurality of radiallydirected slots evenlyspaced about the circumference thereof and openinginto the interior thereof and affording a passage of air into saidrecess across the interior thereof and out the opposite side, and

f. said flat wall having an opening centrally thereof for affordingmovement of air axially of said recess, the air stream moving throughsaid recess between said slots from one side to the other inducing aflow of air through said opening and moving a portion of the air intothe chamber in said body.

1. An ambient air admitting closure member for the ionization chamber ofa combustion product detector comprising: a rigid body having a flatportion and a rim therearound forming a cupped recess therein forproviding one end portion of an ionization chamber, said body having apassage extending through said flat portion centrally thereof andproviding communication between said recess and the ambient air and aplurality of slots spaced around said rim and entering the side of saidrecess, each of said slots being of a configuration for causing ambientair moving toward one side of said body in a path normal to the centralaxis of said chamber and entering said slots to flow over the surface ofsaid flat portion and radially inward toward said central passagewhereby the ambient air from the outside of said body will flow past theinner end of said passage and produce a flow of air through said passageinto said recess transversely of the radial flow of air through saidslots and whereby when ambient air flows axially against said chamber itwill be admitted through said passage and flow from said cup recesstoward said other end of the ionization chamber.
 2. The invention as setforth in claim 1 wherein said flat and rim portions are circular andsaid slots extend radially into said recess.
 3. The invention as setforth in claim 1 wherein said slots extend through the outer peripheryof said flat portion and afford passage of air directly therethroughwhen flowing along paths normal to said flat portion.
 4. The inventionas set forth in claim 2 wherein said slots are equally spaced about saidrim and tend to direct air across said passage regardless of thedirection of flow of the ambient air.
 5. The invention as set forth inclaim 1 including means providing additional peripheral openings intothe chamber adjacent said slots and shielded externally therefrom foraffording a release of air from the chamber.
 6. The invention as setforth in claim 1 including conducting means about said recess forproviding an ion collector plate for the detector.
 7. The invention asset forth in claim 1 having a cup shaped foraminous member within saidcup adjacent the walls thereof for limiting the rate of passage of airthrough said slots.
 8. The invention as set forth in claim 7 whereinsaid foraminous member is a metal screen.
 9. The invention as set forthin claim 8 including means providing an insulated wall chamber openingtoward said cup and having a radiation source therein, and means forproducing an electric potential difference between said screen and saidsource for directing ions toward said screen whereby said screenconstitutes an ion collector plate.
 10. The invention as set Forth inclaim 9 wherein said chamber is cylindrical, and including a circularconducting plate covering a major portion of the bottom wall of saidchamber and in conducting relationship with said source whereby theelectrical field produced by said potential difference is distributedover the cross section of said chamber.
 11. An ion chamber forcombustion product detectors and the like comprising: a body of electricinsulating material having a right circular cylindrical chamber thereinopen at one end and having a flat bottom wall closing its other end, anda flat circular plate in face engagement with said other end concentricwith said cylinder, and means providing a source of alpha particles atthe center of said circular plate, wherein said circular plate coversthe entire area of said bottom wall.
 12. An ion chamber for combustionproduct detectors and the like comprising: a body of electric insulatingmaterial having a right circular cylindrical chamber therein open at oneend and having a flat bottom wall closing its other end, and a flatcircular plate in face engagement with said other end concentric withsaid cylinder, and means providing a source of alpha particles at thecenter of said circular plate, wherein the length of said cylindricalchamber is approximately the same as the diameter thereof and the lengthof the ion chamber is approximately 1 1/4 times the diameter of saidcylindrical chamber.
 13. An ion chamber assembly for apparatus utilizinga radioactive substance for detecting the presence of combustionproducts in the ambient air comprising: a. a body of insulating materialhaving a chamber therein open at one end, b. a closure member for saidopen end, said member having a shallow right cylindrical recessproviding a flat end wall, c. means for holding said body and saidmember in assembled relationship with said chamber and said recess inopen communication and forming a substantially closed ion chamber, d. aradioactive source in said first mentioned chamber, e. the side wall ofsaid closure member having a plurality of radially directed slots evenlyspaced about the circumference thereof and opening into the interiorthereof and affording a passage of air into said recess across theinterior thereof and out the opposite side, and f. said flat wall havingan opening centrally thereof for affording movement of air axially ofsaid recess, the air stream moving through said recess between saidslots from one side to the other inducing a flow of air through saidopening and moving a portion of the air into the chamber in said body.